(a) Normalized amplitude in front of and behind the source and the background noise threshold. (b) Difference between the average amplitudes computed by including and excluding the data under the background noise threshold (); the horizontal line represents the 1 dB limit. (c) MDI values computed by including and excluding the data under the background noise threshold. The values of the MDI computed with all the data and corresponding to a difference in panel (b) lower than 1 dB are highlighted with a thick orange line.